The present invention relates to devices for the fixation and/or support of bones. In particular, the present invention relates to bone support plate assemblies for the fixation and/or support of bones of the spinal column, thus spinal plate assemblies. The plate assemblies of the present invention have particular application in situations where compressional or “settling” forces, as well as torsional and flexing forces on a spinal plate, which supports “fixed” vertebrae, cause significant stressing, and potential failure of the spinal plate and/or plate components.
Vertebral fixation has become a common approach to treating spinal disorders, fractures, and the like, and for fusion of vertebrae at the time such fixation is instituted. Namely, one or more vertebrae are fixed in position relative to one or more other vertebrae above, e.g. toward the head from, and/or below, e.g. toward the coccyx from, the vertebrae being fixed. Generally, a spinal plate is the device of choice used for mechanically supporting such vertebral fixation. A typical spinal plate includes a plate having a plurality of bone support apertures therethrough. A plurality of fasteners, i.e., bone screws, are generally positioned into and through respective bone support apertures of the plate to secure the spinal plate to bone, such as to respective upper and lower supporting adjacent spinal vertebrae. The screws are fastened to the respective support vertebrae to secure the spinal plate to the respective vertebrae. In general, such plate and screw assemblies can be utilized for e.g. anterior fixation of the e.g. cervical, lumbar, and/or thoracic portions of the spine.
The basis of anterior fixation or plating is to approach the spine from an anterior or anterio-lateral direction, and to use the screws to solidly mount the spinal plate to the affected vertebrae. In some instances, in addition to the application of a spinal plate, graft material may be incorporated into the procedure in an attempt to permanently fuse together adjacent vertebrae. The graft material can be e.g. of bone grafts obtained from bones of the recipient or from another individual.
A first common and undesirable result associated with use of conventional such spinal plates is the tendency of the bone screws to “back out,” or pull away from the bone into which they are fixed. This problem occurs primarily as a result of the normal torsional and bending motions of the human body and spine as the recipient/patient goes about routine daily activities. This is a particularly important problem because, as the screws become loose and pull away from the bone, the heads of the screws can rise above the surface of the spinal plate and can even work their way completely out of the bone. While this condition can cause extreme discomfort for the recipient, this condition can also create a number of potentially serious physiological problems given the significant amount of nervous and vascular structures located at or near the potential locations of anterior spinal plate fixations.
A number of designs have been proposed in attempts to prevent screws from pulling away from the bone and/or to prevent the screws from backing out or pulling away from the surface of the spinal plate. Such mechanisms used to prevent bone screws from pulling out of bones include cams which engage and lock the screws, and the use of expanding head screws which expand outwardly when adequate force is applied thereto to engage the holes in the spinal plate. All of these designs have detriments including potential for breakage or requiring particular precision and alignment in their application in order to work correctly. Additionally, loose components and accessories of spinal plates which address the “backing-out” problem can get dropped and/or misplaced while the vertebral fixation surgical procedure is taking place, prolonging and complicating the procedure as well as creating substantial risk of harm to the recipient.
A second common result associated with use of such spinal plates is the tendency of the vertebrae being “fixed” to settle after the spinal plate affixation procedure. Such settling of the “fixed” vertebrae relative to each other is a response to the normal loading of the spine as the recipient/patient carries on routine daily activities. Such settling of the “fixed” vertebrae adds compression forces to the above-listed forces which cause the bone screws to “back out” or pull away from the bone into which they were fixed. Zdeblick et al (U.S. Pat. No. 5,324,290) attempted to address the problem of compression forces in the context of treating vertebral burst fractures, but fails to provide any functional means to prevent the screws pulling away as a result of torsional and flexing forces. Zdeblick et al also fails to provide any structure in the plate assembly which relieves the stress imposed on the plate by the vertebral settling.
My U.S. Pat. No. 6,503,250 teaches use of slot-shaped apertures which enables longitudinal translation of the bone screws in the slot-shaped apertures with respect to the plate in cooperation with post-procedural settling of the vertebrae. Such translation of the bone screws requires that the bone screws not be locked to the plate, and is accompanied by movement of the bone screws with respect to the plate, along the longitudinal axes of the slots, typically along the longitudinal axis of the plate. Such settling of the bones, such movement of the bone screws with respect to the plate, is also accompanied by movement of the plate with respect to one or more of the vertebrae to which the plate is mounted. Such movement of the plate with respect to the bone can, in some instances, have undesirable consequences.
Therefore, it is an object of the invention to provide spinal plate assemblies which accommodate rigid bone-to-bone fixation and provide bone support for such fixation, such as e.g. adjacent or second adjacent vertebrae, while allowing post-procedural compression between the respective bones, e.g. post procedural bone-to-bone movement, without requiring any movement of any bone screw in a slot-shaped aperture with respect to the respective plate.
It is a further object of the invention to provide spinal plate assemblies wherein the bone screws do not need to move with respect to the plate assembly in order for stress, potentially imposed on the plate assembly by post-procedural settling of the vertebrae, to be relieved or avoided.
Yet a further object of the invention is to provide spinal plate assemblies having first and second sliding plates which are adapted and configured to provide plate-on-plate sliding of the first and second plates, with respect to each other, in order to relieve a substantial portion of the stress which would otherwise be imposed on the respective plate assembly by post-procedural vertebral settling.
Still a further object of the invention is to provide spinal plate assemblies which accommodate bone-to-bone settling while providing bone support for such fixation, while accommodating post procedural compression between the respective bones, and while maintaining rigid, unmoving fixation between the plate and the respective bones/vertebrae.
It is a further object of the invention to provide bone support plate assemblies, e.g. spinal plate assemblies, which accommodate bone-to-bone settling while providing bone support for such fixation, while accommodating post procedural compression between the respective bones, without requiring, or enabling, any movement of any plate with respect to a bone to which such plate is mounted.